UNIVERSITY   OF   CALIFORNIA  agricultural  ExperimentStation 

College  of  agriculture  e.  j.  wickson,  acting  director 

BERKELEY,  CALIFORNIA 

CIRCULAR  No.  18 

(February,  1906) 


CATERPILLARS  ON  OAKS 


BY 

C.  W.  WOODWORTH. 


The  live-oaks  about  the  Bay  region  of  California  are  subject  from 
time  to  time  to  the  attack  of  immense  swarms  of  caterpillars,  which 
often  entirely  defoliate  them,  thus  rendering  them  temporarily  un- 
sightly and  contributing  in  no  small  measure  to  the  death  of  the  trees. 
These  losses  can  be  entirely  avoided,  however,  if  the  proper  measures 
are  taken,  and  this  circular  is  prepared  to  call  attention  to  the  methods 
of  accomplishing  this  work. 

There  are  two  species  concerned,  which  have  quite  different  habits 
and  present  a  somewhat  different  problem  of  control. 

1.     California  Oak  Caterpillar. 

(Phryganidia  calif omica,  Pack.) 

The  insect  bearing  the  above  scientific  name  might  be  called  the 
"California  oak  caterpillar,"  since  it  is  strictly  limited,  as  far  as 
known,  to  this  tree.  It  is  a  remarkable  moth  in  many  ways ;  it  is  not 
found  outside  of  California,  and  is  the  only  representative  of  its  family 
in  America.  The  moth  is  pale  gray  in  color  with  an  expanse  of  wings 
of  about  an  inch,  and  can  be  seen  sometimes  in  countless  numbers 
flying  about  oak  trees,  especially  in  the  latter  part  of  the  day.  They 
are  not  strong  of  wing,  but  simply  flutter  about,  alighting  now  and 
then  on  leaves  and  then  again  taking  to  wing.  During  the  night  and 
the  larger  part  of  the  day  most  of  the  individuals  will  be  found  resting 
quietly  on  the  leaves.  The  length  of  life  in  this  stage  of  its  existence 
is  somewhere  in  the  neighborhood  of  two  weeks,  during  which  time  it 
may  lay  two  or  three  masses  of  eggs,  or  sometimes  deposit  all  of  its 
eggs  in  one  place.  The  under  sides  of  the  leaves  are  usually  chosen  for 
egg  laying.  The  eggs  are  about  the  size  of  a  radish  seed,  yellow 
in  color  at  first  but  become  darker  as  they  develop,  and  finally  the 
caterpillar  emerges  and  begins  to  feed  upon  the  foliage.     The  first 


feeding  is  usually  on  the  under  side  of  the  leaves  and  is  noticeable  on 
the  upper  side  only  as  pale  spots  due  to  the  drying  out  of  the  leaf  over 
the  denuded  portion  beneath  caused  by  their  feeding.  Later,  however, 
when  the  caterpillars  get  larger,  the  leaf  is  eaten  through  except  along 
the  larger  veins,  and  thus  becomes  skeletonized.  The  leaves  so  eaten 
usually  soon  drop  from  the  tree,  which  thus  becomes  entirely  devoid 
of  foliage.  This  may  sometimes  occur  before  the  larger  part  of  the 
caterpillars  have  finished  feeding,  and  they  may  die  of  starvation. 
Usually,  however,  a  good  proportion  of  them  find  enough  to  bring 
them  to  maturity.  They  then  seek  a  suitable  spot  on  the  bark  of  the 
tree  and  transform  into  a  chrysalis,  which  is  more  like  that  of  a  but- 
terfly than  the  form  common  in  moths,  and  is  entirely  naked,  not  being 
protected  by  silken  coverings.  This  chrysalis  is  strikingly  ornamented 
with  black  marks  and  is  really  a  very  beautiful  object.  After  a  short 
time  in  this  stage  the  adult  moth  emerges,  thus  completing  the  cycle. 

The  remedy  for  this  insect  is  to  spray  the  trees  with  paris  green, 
using  a  mixture  of  one  pound  of  paris  green  to  two  hundred  gallons 
of  water.  When  the  moths  are  seen  fluttering  about  the  tree  in  great 
numbers  immediate  arrangements  should  be  made  for  spraying  the 
trees,  and  strict  watch  maintained  so  as  to  recognize  the  first  signs  of 
injury  by  the  young  worms  produced  from  this  brood  of  moths.  As 
soon  as  these  worms  are  noticed  the  application  should  be  made  at 
once  and  with  great  thoroughness,  so  as  to  place  some  of  the  poison  in 
reach  of  every  caterpillar.  If  this  is  done  the  insects  will  be  killed 
before  serious  injury  is  occasioned  and  a  single  application  will  control 
the  difficulty.  This  has  been  demonstrated  many  times  in  many  places, 
so  that  there  is  no  doubt  of  the  efficiency  of  the  treatment.  In  most 
cases  in  the  past,  however,  the  mistake  has  been  made  of  allowing  the 
caterpillar  to  become  large,  so  that  considerable  damage  is  done  to  the 
trees  before  any  steps  are  taken  toward  controlling  it.  There  should 
be  no  difficulty,  however,  in  following  the  directions  here  given,  be- 
cause the  presence  of  the  moth,  which  everybody  recognizes,  indicates 
the  approach  of  the  injury  and  gives  ample  time  for  the  preparations 
for  the  work. 

In  spraying  for  this  insect  the  only  difficulty  met  with  is  that  de- 
pendent upon  the  size  of  the  trees  affected.  It  will  usually  be  neces- 
sary, in  order  to  effectively  spray,  to  provide  ladders  and  send  the 
man  using  the  nozzle  into  the  highest  parts  of  the  tree,  and  to  provide 
him  with  a  long  extension  rod  enabling  him  to  reach  to  every  part, 
since  thorough  work  can  be  done  in  this  way  only.  One  should  use  a 
spray  nozzle  giving  a  fine  mist,  and  never  attempt  to  spray  a  tree  with 
a  nozzle  which  throws  a  stream,  for  thorough  spraying  cannot  be  ac- 
complished in  that  way.  All  good  spray  nozzles  are  short-distance 
nozzles  and  must  be  placed  close  to  the  parts  of  the  tree  when  they  are 
being  sprayed.  Furthermore,  in  spraying  these  insects  the  trees  should 
never  be  allowed  to  drip,  because  after  the  leaves  have  been  thoroughly 
wetted  with  a  fine  mist  any  further  application  simply  washes  off  the 
poison  which  has  already  been  placed  on  them,  and  a  much  less  satis- 
factory distribution  of  the  poison  results. 


Thorough  spraying  requires,  then,  first,  the  reaching  of  every  part 
of  the  tree ;  second,  the  use  of  a  spray  nozzle  giving  a  fine  mist ;  and, 
third,  the  avoidance  of  drip. 

The  University  is  now  experimenting  with  the  use  of  especially 
large  sizes  of  extension  rods  with  the  hope  of  finding-  satisfactory 
means  of  handling  rods  that  will  reach  the  topmost  parts  of  the  tree, 
avoid  the  use  of  ladders,  and  so  simplify  the  spraying  problem ;  and 
if  the  experiments  prove  successful  the  matter  will  be  reported  in  full 
in  a  bulletin  of  this  Station,  but  there  need  be  no  failure  to  protect 
the  trees  if  one  is  sufficiently  interested  to  give  the  necessary  labor  and 
attention. 

2.     Tent  Caterpillars. 
Malacosoma,  spp. 

The  above  name  applies  to  a  series  of  moths,  some  six  in  number, 
which  are  usually  known  by  the  term  "tent  caterpillar,"  because  of 
the  peculiar  habit  of  the  young  caterpillar  of  constructing  silken  tents 
in  which  they  live  the  larger  part  of  the  day,  only  going  forth  from 
time  to  time  to  feed  upon  the  leaves.  The  six  species  known  to  occur 
in  California  are  very  similar  in  appearance  and  habits,  though  some 
show  such  a  remarkable  amount  of  variation  in  color  and  pattern  of 
the  wings  of  the  moth,  that  they  have  received  quite  a  number  of 
names,  and  a  good  many  varieties  are  recognizable. 

The  insects  are  not  strictly  confined  to  the  oak;  indeed  most,  if 
not  all  of  them,  are  rather  general  feeders.  In  the  Bay  region  the 
live-oak  leaf  seems  to  be  a  favorite  food,  so  that  often  they  are  se- 
riously troublesome  on  the  oak  and  scarcely  noticeable  on  the  other 
trees.  The  moth  is  quite  strictly  a  night  flier  and  is  not  very  com- 
monly observed.  The  eggs  are  laid  in  a  mass  upon  the  small  twigs, 
usually  forming  a  ring  around  the  twig,  though  some  times  occurring 
simply  as  a  mass  on  one  side  of  the  branch.  The  eggs  are  somewhat 
conical,  set  with  the  small  end  toward  the  twig  and  all  firmly  cemented, 
so  that  the  individual  eggs  are  not  usually  easy  to  distinguish.  These 
insects  are  not  at  all  infrequent  on  orchard  trees  all  over  the  State, 
and  the  egg  masses  are  known  to  all  orchardists  who  come  across  them 
in  pruning  in  the  winter.  The  insects  are  all  strictly  one  brooded, 
passing  the  winter  in  the  egg  state.  Quite  early  in  the  spring  the 
eggs  hatch  and  the  worms  produced  proceed  at  once  to  a  crotch,  usually 
following  down  the  twig  and  selecting  the  crotch  where  this  twig  joins 
another,  and  there,  all  working  together,  build  a  tent  of  silk  in  which 
they  hide.  This  tent  at  first  is  quite  small  but  is  increased  day  by 
day  and  serves  as  ample  protection  for  the  growing  worms.  When  the 
food  is  abundant  the  insects  may  spend  the  larger  part  of  their  life  in 
this  tent,  living  together  as  a  large  family,  going  out  in  droves  and  feed- 
ing together  and  returning  again  together  to  their  tent ;  but  when  food 
is  scarce  the  social  instinct  is  gradually  overcome  and  the  insects  may 
be  found  wandering  all  over  the  trees,  and  leaving  the  tree  to  attack 
other  plants.  In  all  cases  when  the  insect  is  nearly  full-grown  this 
wandering  habit  is  assumed,  even  though  the  food  may  be  ample ;  and 


wherever  they  are  abundant  they  become  very  conspicuous  through 
their  habit  of  crawling  over  the  ground,  especially  along  paths  and 
sidewalks,  and  even  crawling  up  sides  of  buildings.  Finally  they  spin 
cocoons  over  themselves,  using  the  hairs  that  cover  the  body  in  addi- 
tion to  the  silk  which  they  spin,  and  then  transform  into  the  pupa 
condition,  from  which  somewhat  later  the  moth  emerges,  and  after 
living  its  retiring  life  lays  its  mass  of  eggs  and  dies. 

The  control  of  this  insect  on  smaller  trees  when  not  very  abundant 
can  often  be  best  accomplished  by  searching  for  the  tents  in  the 
crotches  in  the  spring  and  the  destruction  of  each  colony.  In  the 
Eastern  States  a  chemist's  test  tube  brush  attached  to  the  end  of  a 
long  pole  is  often  used,  by  means  of  which  the  small  tents  can  be 
brushed  out  of  the  tree  and  brought  down  with  their  contents  of  small 
worms.  The  use  of  a  torch  consisting  of  a  rag  tied  in  a  ball  at  the  end 
of  a  pole  and  saturated  with  kerosene  and  set  on  fire  has  been  quite 
commonly  used  in  California  for  the  burning  out  of  the  tents,  but  is 
no  more  rapid  than  the  brush  method  and  endangers  the  life  of  the 
twigs.  We  would  be  rather  inclined  to  use  the  pole  pruning  shears 
and  remove  the  twigs  entirely,  rather  than  to  use  the  torch  method. 
When  the  insects  are  very  abundant  it  will  often  be  preferable  to  spray 
the  trees  in  the  same  way  as  for  the  preceding  insect.  The  spray 
method  to  be  employed  is  exactly  the  same  as  for  the  Phryganidia, 
and  the  timing  of  the  spray  should  depend  upon  the  observation  of 
the  presence  of  the  small  tents  produced  by  the  newly  hatched  worms. 
If  the  spraying  is  attended  to  while  the  tents  are  still  small  there  will 
be  no  appreciable  damage  to  the  trees,  but  if  this  matter  is  allowed  to 
go  on  until  the  insects  are  nearly  full-grown  there  may  not  be  enough 
good  accomplished  in  spraying  to  pay  for  the  treatment. 

Concluding  Remarks. 

The  oak,  which  is  our  most  beautiful  native  tree  in  central  Cali- 
fornia, should  be  protected  from  its  insect  enemies.  This  can  be  done 
by  spraying  with  paris  green.  Any  kind  of  spray  outfit  will  do, 
though  on  account  of  the  large  size  of  the  trees  it  would  be  distinctly 
desirable  to  have  the  use  of  a  power  outfit.  The  maintenance  of  the 
beauty  of  the  shade  trees  is  a  community  matter  and  it  would  be  wise 
for  the  Street  Departments  of  cities  to  be  provided  with  ample  equip- 
ment for  making  such  applications.  In  villages  and  country  places 
the  ordinary  orchard  spray  outfit  is  already  at  hand  and  can  be  used. 
Success  will  depend  upon  the  thoroughness  and  the  proper  timing  of 
the  treatments. 


